Personalized attention +34 96 206 62 98
Free shipping to Iberian Peninsula from 30€
9/10 Rating
Discreet shipping
Powdery mildew is a fairly common pest that affects marijuana crops and can cause serious damage to the plants, affecting their health irreversibly. It is a fungus with a recognizable appearance, similar to a white powder covering the leaves, stems, and even the buds. If no measures are taken at the first signs of infection, the fungus will spread quickly, causing the leaves to yellow and wrinkle.
What is powdery mildew
Powdery mildew is a type of parasitic fungus that belongs to the Erisifaceae family. It affects a wide variety of plants, especially agricultural, ornamental, and fruit crops. It is described as an ectoparasitic fungus, meaning it does not deeply penetrate plant tissues but instead extracts nutrients from the surface cells using structures called haustoria.
How it spreads
This fungus reproduces through spores that spread through the air, by contact, or from plant to plant. This makes it spread very easily, since if a plant affected by powdery mildew reaches your grow, the disease will likely spread quickly to the rest. This fungus thrives in spring and usually disappears in summer. The main problem with powdery mildew is that it is very resistant, and once it appears, eradicating it is difficult, requiring constant treatment until the end of the harvest.
How to identify it
Powdery mildew can be identified with the naked eye, and it’s important to inspect the plant regularly because this fungus can attack every year, so you should never let your guard down. The problem is that by the time you can spot powdery mildew, there are already thousands or millions of spores covering the crop’s plants.
At first, the infestation appears as small white spots that look like ash or dust, but they are spores. Under a microscope, these flour-like patches reveal conidia—or spores—white and hair-like, resembling grass. Powdery mildew is often confused with another fungus that attacks cannabis: downy mildew. In reality, downy mildew typically forms on the underside of the leaves and appears in more extreme environments. Below are the main differences between powdery mildew and downy mold.
| Characteristic | Powdery Mildew | Downy Mildew |
| Pathogen | Fungus from the class Ascomycota (genus Erysiphe, Podosphaera, etc.) | Fungus or oomycete from the class Oomycota (genus Plasmopara, Peronospora, etc.) |
| Appearance | Whitish or grayish powder on leaves, stems, and fruits. | Yellowish or oily spots on the leaf surface and white or gray mold on the underside. |
| Favorable conditions | High relative humidity (50–70%) and moderate temperatures (15–25 °C). Doesn’t require free water. | High humidity (80–100%) and presence of free water (dew or rain). Temperatures between 10–20 °C. |
| Affected parts | Mainly leaves, stems, flowers, and young fruits. | Mainly leaves and sometimes stems or fruits. |
| Spread | Wind-borne spores. | Water- and wind-borne spores. |
| Damage | It reduces photosynthesis, weakens plants, and affects fruit development. | Causes leaf necrosis, defoliation, and in severe cases, plant death. |
| Preventive control | Improve ventilation, prune, and use specific fungicides (sulfur, triazoles). | Manage irrigation, remove infected leaves, and use fungicides (copper, phosphites). |
Differences between powdery mildew and downy mildew.
Will powdery mildew fungus disappear if the plant is cut?
If powdery mildew is detected on a plant, it’s a good idea to remove the affected parts as soon as possible. That means cutting off infected leaves, flowers, or branches. If done in time, this can prevent the fungus from spreading to other parts of the plant (and nearby plants, if any). The issue is that since it’s a microorganism, we can’t be sure it’s completely gone, so in addition to pruning, it’s best to use a fungicide product to ensure full elimination.
What happens if you smoke powdery mildew
Another problem caused by powdery mildew infection in marijuana plants is that if any affected buds are consumed, they can damage the respiratory system. When smoked, you won’t notice anything unusual—just a harsher taste—but if the fungus enters your lungs, it can cause lung infections, asthma, and more serious illnesses.
What precautions to take during a powdery mildew infestation
If your grow is affected by powdery mildew, in addition to removing the infected parts, you must take important precautions to prevent further spread.
- Always wear a mask to avoid inhaling spores.
- Wear special clothing when entering the grow area and change before leaving to avoid carrying spores with you.
- Wash your hands thoroughly after handling the plants.
- Don’t allow others to visit the grow.
How to get rid of powdery mildew fungus for good?
There are several strategies we must follow to try to eliminate powdery mildew before it wipes out our plants.
Control the temperature
The first step is to control the temperature, knowing that powdery mildew prefers 15–30ºC. At 35ºC, it begins to decline since high heat destroys its spores. Below 5ºC, growth is also inhibited, although note that powdery mildew can stay dormant through winter, waiting for the right conditions.
Control humidity
Humidity is a key factor for fungal growth in general, including powdery mildew. So, one way to prevent and stop its spread is to avoid spraying and instead water directly into the soil to prevent moisture on the leaves.
Improve ventilation
Air circulation in the grow is also important to prevent powdery mildew. Plants should be spaced out to allow enough room and airflow. This is especially crucial for greenhouse or indoor grows, where poor ventilation often makes plants more vulnerable to fungi.
Use insecticides and fungicides
Once powdery mildew is present, it’s highly recommended to use a fungicide. There are natural treatments that work well, such as sulfur, baking soda, potassium soap, propolis, or horsetail.
Natural treatments to fight powdery mildew fungus
These are the most effective natural products against powdery mildew. They can also be used preventively, along with the measures we’ve described earlier.
Horsetail
It’s rich in silica, which strengthens plant structure and increases resistance to pests. Boil 100g of fresh plant in 1 liter of water for 20 minutes, let cool and strain. Dilute with water in a 1:5 ratio and spray weekly if infected, or every two weeks as a preventive measure.
Sulfur
Dust directly onto the plants or mix with water. Don’t apply in temperatures over 30ºC to avoid burns.
Copper
Copper compounds like copper oxychloride or copper sulfate are commonly used to fight fungal infections. Follow the manufacturer’s instructions for use.
Potassium soap
Insecticide and antifungal. Mix 10–20 ml of soap per liter of water and spray directly once a week.
Propolis
This bee product strengthens plant structure and has antifungal properties. Dilute 1 or 2 ml of propolis extract in 1 liter of water and spray once a week.
Baking soda
It alters the pH of the leaf surface, preventing fungus development. Dilute 1 teaspoon of baking soda in 1 liter of water and spray once a week.
Garlic infusion
Garlic has natural antifungal properties thanks to a compound called allicin. Crush 5–6 garlic cloves and boil in 1 liter of water for 10 minutes. Let cool and strain. Spray infected leaves every 5–7 days.
Hydrogen peroxide
Hydrogen peroxide eliminates powdery mildew by oxidizing fungal cells and destroying spores on leaf surfaces. Mix 1 part 3% hydrogen peroxide with 4 parts water (e.g., 250 ml of peroxide in 1 liter of water). If using stronger peroxide (6% or more), dilute further to avoid damaging the plant. Place the mix in a clean spray bottle and apply every 3 days until the fungus is gone.
Besides these natural remedies, you can also find specific products to combat powdery mildew. Many are made from natural ingredient blends that are highly effective.
